The Journal of Indian Botany/Volume 1/March 1920/The Physiological Anatomy of the Plants of The Indian Desert
THE
Journal of Indian Botany.
Vol. I. MARCH, 1920. Nos. 6 & 7
THE PHYSIOLOGICAL ANATOMY OF THE
PLANTS OF THE INDIAN DESERT
BY
T. S. Sabnis, B.A., B.Sc.
St. Xavier's College, Bombay.
(Continued from p. 169.)
ZYGOPHYLLACEAE.
Tribulus terrestris L.— Figs. 68, 69, 70. Epidermal cells tabular with outer and inner walls convexly arched outwards and inwards, respectively. Guard-cells elevated. Veins embedded and provided with bundle-sheaths, of thick-walled chlorophyll containing cells. Mesophyll composed of palisade tissue on the adaxial side and of subepidermal aqueous layer and palisade tissue on the abaxial side. Clustered crystals occurring in the leaf and axis. Clothing hairs unicellular on the leaf and axis. Primary cortex forming an aqueous tissue. Wood composite. Wood prosenchyma enclosing the end of the xylem bundles. Pith formed of thick-walled cells.
Tribulus alatus L.— Epidermal cells tabular with outer and inner walls convexly arched outwards and inwards respectively. Outer walls superficially granulated. Guard-cells elevated. Mesophyll formed of palisade tissue on the adaxial side and subepidermal aqueous layer and palisade tissue on the abaxial side. Veins embedded and provided with bundle-sheaths of thick-walled chlorenchymatous cells. Clustered crystals in the leaf and axis. Wood composite. Wood parenchyma enclosing the lower ends of the xylem bundles, Pith. formed of thin-walled cells.
Seetzenia orientalis Dene —Figs. 71, 72, 73, 74. Epidermal cells tabular, Large water-storing cells intercalated amongst the ordinary epidermal cells. Stomata depressed. Mesophyll formed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Veins not provided with bundle-sheaths. Clustered crystals occurring in the leaf and axis. Assimilatory tissue in the axis formed of chlorenchyma. Wood composite. Pith formed of thin-walled cells and forming occasionally an aqueous tissue.
Zygophyllum simplex L. Figs. 75, 76. Epidermal cells polygonal. Guard-cells elevated. Mesophyll composed of a subepidermal composite ring of palisade cells enclosing a massive aqueous tissue surrounding the central vascular bundles. Veins embedded. Peripheral veins numerous, strengthening the aqueous tissue and provided with sheaths of thick-walled cells, the outer ones containing chlorophyll and the inner ones containing clustered crystals. Veins traversing the aqueous tissue. T. S. of the axis kidney-shaped with angles projecting outwards at the grooved surface. Primary cortex forming an aqueous tissue. Wood composite. Pericycle distinctly isobilateral. Pith of thin-walled cells and forming an aqueous tissue. Clustered crystals numerous in the axis.
Fagonia cretica L. Figs. 77, 78. Epidermal cells with outer and inner walls convexly arched outwards and inwards. Outer walls superficially granulated. Guard-cells elevated. Mesophyll isobilateral. A group of palisade like cells faintly green and perhaps with a water-storing function, occurring between the lower epidermis and the vein of the mid-rib. Oxalate of lime not occurring in any form. Veins embedded and provided with bundle-sheaths of thin-walled cells. Assimilatory tissue in the axis formed of palisade cells. Wood composite. Pith formed of thin-walled cells.
Structure of the Axis.—The epidermis consists of tabular cells with outer and inner walls convexly arched outwards and inwards respectively. The lateral walls are usually straight. The outer walls are superficially granulated in Tribulus alatus, Fagonia cretica and Zygophyllum simplex. Large water-storing cells are intercalated amongst the ordinary epidermal cells in Seetzenia orientalis (fig. 71). Epidermal cells are thin- walled ; this can be accounted for by the fleshy character of the leaves.
The stomata occur on both the surfaces, though more numerous on the lower; they are surrounded by 3-6 ordinary epidermal cells. Guard-cells are elevated in species of Tribalus, Fagonia cretica Zygophyllum simplex (fig. 75), so that the front-cavity is on a level with the surface. In Seetzenia orientalis (fig. 72), the stomata are depressed and the guard-cells are either in the same plane or in a plane lower than that of the surrounding cells.
The elevated position of the stomata in species of Tribulus may be due to a protective covering of hairs and to the subepidermal aqueous tissue on the lower side, in F. cretlca to a comparatively extensive ventilating system and to the glandular' nature of the plant and in Zygophyllum simplex; to the abundance of aqueous tissue. The depressed position of the stomata in S. orientalis is perhaps clue to the absence of aqueous tissue in the mesophyll.
The mesophyll in species of Tribulus (fig. 68) is composed of a layer of long palisade cells on the upper side and of a subepidermal layer of polygonal aqueous cells and a layer of short palisade cells on the lower; the middle tissue is represented by the chlorenchymatous cells of the bundle-sheaths. In the cylinderical leaves of Z. Simplex, the assimilatory tissue forms a subepidermal composite ring of palisade cells and encloses a massive aqueous tissue of large thin-walled cells, which surrounds the central vascular bundles. In Scetzenia orientalis (fig. 71) there is a two-layered palisade tissue on the adaxial side and a two-layered arm-palisade tissue on the abaxial side; the middle tissue consists of thin-walled polygonal cells, some of which contain clustered crystals. The mesophyll in F. cretica (fig. 77) is composed of palisade tissue on both the sides with the middle tissue represented by the bundle-sheath cells. In F. cretica there occur rounded groups of faintly green palisade-like cells, with perhaps a water-storing function, between the lower epidermis and the vein of the mid-rib. Internal secretory organs do not occur in any of the members.
Oxalate of lime occurs in the form of clustered crystals in the neighbourhood of the veins in species of Tribulus, S. orientalis and Z. simplex in which the inner cells of the sheaths of the peripheral veins mostly contain clustered crystals (fig. 75).
The veins are embedded and are provided with green bundle- sheaths. The sheeth cells are thin-walled and polygonal in F. cretica they are cubical and thick-walled in the other members of the order The veins are numerous in species of Tribulus, F, cretica and Z. simplex. The abundance of veins corresponds with the abundance of watery contents in the mesophyll. The peripheral veins in Z. simplex form a supporting network of veins* for the massive aqueous tissue.
Hairy covering is present only on the leaf and axis, in species of Tribulus. It consists of simple unicellular hairs which are more numerous on the lower surface of the leaf (figs. 68, 69). External glands are not found on any of the members.
Structure of the Axis. — Epidermis in species of Tribulus consists of small thick-walled cells. The epidermal cells in S. orientalis are polygonal with outer and inner walls thickened and with lateral walls thin and undulated : there are large cells, perhaps with a waterstoring function, intercalated amongst the ordinary epidermal cells (fig. 73), Epidermal cells in F. cretica are tabular with outer walls thickened and cuticularised and with lateral walls thin and straight, Epidermis in Z. simplex is composed of polygonal cells with outer walls thickened and papillose. Outer walls are superficially granulated in all members except T. terrestris. The stomata are like those on the leaf.
The primary cortex in species of Tribulus is characterised by the presence of a layer of subepidermal collenchyma below which occurs cortical parenchyma with a water-storing function. The cortex in S. orientalis consists of chlorenchyma and forms an assimilatory tissue; it forms an aqueous tissue strengthened in the projecting angular portions by small stone-cell groups in Z. simplex. In F. cretica it consists on its outer side of an assimilatory tissue of palisade cells and of an inner portion of an aqueous tissue; it is strengthened by stone-cell groups which can be roughly arranged in three rings, the outermost groups being the largest and almost subepidermal in position and giving a ribbed appearance to the axis.
The pericycle is composed of rhomboidal groups of stone-cells in species of Tribulus, S. orientalis and F. cretica. The stone-cell tissue is extensive and is necessary to strengthen the massive cortical aqueous tissue. The pericycle in Z. simplex is composed of stone-cell groups and presents an isobilateral arrangement; the stone-cell tissue along the grooved portion is greatly reduced and consists of isolated stone-cells or of very small groups.
In prostrate axis of species of Tribulus and of S. orientalis the stone-cell tissue is more extensive along the upper portion of the axis. In spite of the prostrate habit of the axis of F. cretica the pericycle does not seem to be much affected except that the stone-cell groups are closer together on the upper side.
The structure of the wood presents an isobilateral appearance in all the members. Wood forms a composite hollow cylinder formed of closely placed xylem bundles. Interfascicular wood prosenchyma is little developed. Wood prosenchyma encloses the lower portion of the xylem bundles in T. terrestris, while in T. alatus it is replaced by wood parenchyma; this may form a specific difference. Medullary rags are absent except in F. cretica where uniseriate rays occur.
Along the upper surface which is more exposed to the sun and climatic factors and which consequently presents greater functional activity, the xylem bundles are larger with vessels larger and more numerous; on the lower side which is protected from the sun the xylem bundles are much smaller and the vessels smaller and less numerous. The prostrate habit even affects the symmetry of the whole axis in F. cretica and Z. simplex where the axis is semi-terate and presents a kidney-shaped appearance in T. S., the grooved surface representing the side in contact with the substratum.
Soft bast forms a continuous ring and follows the outline of the wood cylinder. Oxalate of lime is found in the form of clustered crystals in the cortex and pith in the species of Tribulus and T. orientalis. Pith consists of thick-walled cells in species of Tribulus and F. cretica; in others it is composed of thin-walled cells' The pith in S. orientalis and Z. simplex may occasionally form an aqueous tissue.
General Review. — The plants are fleshy and characterised by the plasticity of the tissues as was seen in the different modifications introduced in the prostrate axis. Outer walls of the epidermal cells are not much thickened and are superficially granulated. There is abundance of aqueous tissue in the leaf and axis. Mesophyll is truly isobilateral and shows a distinct tendency to isobilateral symmetry. Hairs, when present, are unicellular. Guard-cells are elevated, so that the front cavity is on a level with the surface, with the exception of S. orientalis, where the stomata are depressed. The veins, are embedded and provided in some members with distinct bundle-sheaths. Oxalate of lime-occurs in the form of clustered crystals in the leaf and axis.
The assimilatory tissue is composed either of palisade cells or of chlorenchyma or is absent, in which latter case the primary cortex functions as an aqueous tissue. The pericycle is composed of groups of stone-cells and presents an isobilateral structure. Wood forms a composite hollow cylinder. Medullary rays occur only in F. cretica and are uniseriate. The size of the xylem bundles and the size and abundance of vessels vary on the upper and lower surface of the prostrate axis. Soft bast forms a continuous ring and follows the outline of the wood cylinder.
The pith is composed of thick-walled or thin-walled cells. In the latter case the pith may occasionally form an aqueous tissue.
GERANIACEAE.
Monsonia heliotropioides Boiss.— Plate X figs. 79, 80, 81. Leaf only. Epidermal cells polygonal with outer walls papillose especially so on the lower surface. Inner and outer walls equally thickened. Stomata occurring on both the surfaces and surrounded by ordinary epidermal cells. Guard-cells elevated. Mesophyll formed of greatly elongated palisade cells on the upper side and of arm-palisade tissue on the lower. Internal glands absent. Clothing hairs lular and with muriculate walls. Glandular hairs formed of a short uniseriate stalk and of an obconical unicellular head. Oxalate of lime found in the form of clustered crystals. Leaf many-ribbed. Veins of the ribs vertically transcurrent. Smaller veins embedded.
Structure of the Leaf.—The epidermal cells are polygonal with outer walls papillose much more so on the lower surface. The outer and inner walls are equally thickened. Inner walls are convexly arched inwards, thus coming into close contact with the assimilatory tissue. The lateral walls are thin and undulated. The stomata are more numerous on the lower surface and are accompanied by ordinary epidermal cells. Guard-cells are situated in the plane of the outer epidermal walls ; and the front cavity Ms on a level with the surface.
The hairy covering consists of clothing and glandular hairs the former are more numerous on the lower surface and the latter more numerous on the upper. The clothing hairs are unicellular and have muriculate walls; the basal portion is conical and is inserted between the epidermal cells (figs. 79, 81). Glandular hairs are formed of a short uriseriate stalk and of an obconical head (figs. 79, 80).
The mesophyll is composed of a layer of very long palisade cells on the adaxial side and of an arm-palisade tissue on the abaxial side. The elongated form of the palisade cells affords protection, against intense light, to the chlorophyll grains. The greatly elongated palisade cells, the development of arm-palisade tissue and the thickening of the outer and inner epidermal walls are distinct proofs of xerophytic characters developed by the plant. Internal secretory organs are not found in the leaf or axis. Oxalate of lime occurs in the form of clustered crystals near the veins.
The leaves are many-ribbed. The ribs are prominent below and grooved above. The veins of the ribs are vertically transcurrent above by colourless parenchyma and below by collenchyma. Smaller veins are embedded. Bundle-sheaths are not found round the veins
SIMARUBACEAE.
Balanites Roxburghii Planch.— Figs. 82. 83, 84. Epidermal cells of the leaf and axis tabular. Mesophyill-bifacial. Stomata depressed with guard-cells below the plane of the surrounding cells. Internal glands absent. Oxalate of lime found in the form of solitary and clustered crystals in the leaf and axis. Veins embedded and enclosed in bundle sheaths. Groups of water-storing tracheids occurring at intervals between the veins. Clothing hairs present in the form of short thick-walled unicellular trichomes. Glandular hairs absent. Assimilatory tissue in the axis formed of chlorenchyma. Cortical parenchyma with numerous water-storing tracheicls. Pericycle formed of small groups of stone-cells. Vessels small and few. Interfascicular wood prosenchyma extensive. Medullary rays 1-2 seriate Xylem bundles occurring in the soft bast. Pith characterised by sieve-sclereids.
Structure of the Leaf.—The epidermal cells are tabular with outer and inner walls convexly arched outwards and inwards respectively. The outer walls are thickened. The cuticle is striated. The lateral walls are thin and straight. The stomata are depressed and are more numerous on the lower surface and are surrounded by ordinary epidermal cells. Guard-cells are situated in a plane a little below that of the surrounding cells (figs. 82, 84).
The mesophyll is composed of palisade tissue on the upper side and of spongy on the lower. Internal glands do not occur in the leaf and axis. Oxalate of lime occurs in the leaf in the form of solitary crystals and clustered crystals near the veins of the leaf and in the cortical parenchyma of the axis. The veins are embedded and are provided with green bundle- sheaths; they are protected on the lower side by sclerenchyma. There are numerous groups of water-storing tracheids with pitted markings, occurring at intervals between the veins.
The hairy covering on the leaf and axis consists of thick-walled unicellular straight or bent trichomes (figs. 82, 84.) External glands do not occur on the leaf and axis.
Structure of the Axis.— Epidermis 'consists of small vertically tabular cells with outer walls greatly thickened and convexly arched outwards. Cuticle is striated. The cortex is composed of arm-palisade tissue on its outer side and of colourless cortical parenchyma on the inner. The cortical parenchyma is distinguished by the presence of sclereids with concentric stratification and radial lamellae.
The pericycle is composed of small groups of stone-cells. The wood forms a composite hollow cylinder. The vessels are small and are arranged in incomplete rows. The interfascicular wood prosenchyma is extensive and is composed of thick-walled cells with small lumina. The medullary rays are 1-2 seriate. A few xylem bundles occur in the soft bast (fig. 83 ) and form an anomolous structure in the axis.
The pith is characterised by sieve sclereids (fig. 83) and is composed of thick-walled cells.
BURSERACEAE.
Commiphora Mukul Engl— Plate XI, Fig. 85. Epidermal cells of the l«aves with innerwalls gelatinised. Stomata present on both the surfaces. Guard cells elevated. Mesophyll composed of palisade tissue on the upper side and of arm-palisade tissue on the lower, Balsam canals found in the phloem of larger veins and in the soft basli of the axis. Pith cells with tanniniferous contents. Oxalate of lime occurring in the form of solitary, clustered and conglomerate crystals. Larger veins vertically transcurrent below by collenchyma. Hairy covering consisting of a few uniseriate trichomes. Cork subepidermal. Assimilatory tissue in the axis formed of chlorenchyma. Vessels large and few. Medullary rays uniseriate and numerous. Sclerenchyma enclosing the lower ends of the xylem bundles. Xylem bundles found in the soft bast. Pith characterised by numerous sievo-sclereids.
Structure of the Leaf.—The epidermal cells are horizontally tabular with inner walls gelatinised and outer walls fiat and thickened. They are secondarily divided by thin cross walls beneath which a mucilaginous mass is found. The lateral walls are thin and straight. The stomata are surrounded by ordinary epidermal cells and are more numerous on the lower surface. The guard-cells are elevated and the front cavity is on a level with the surface.
The mesophyll is composed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Some of the palisade cells possess little chlorophyll and break down into cavities in dried material. Small scattered groups of sclerenchyma occur below the lower epidermis.
The internal secretory organs are represented by balsam canals in the phloem of the larger veins and in the soft bast in the axis (fig. 85 B.C.) There are numerous pith cells with tanniniferous contents. Oxalate of lime occurs in the form of solitary crystals near the veins. In the axis solitary as well as clustered and conglomerate crystals are found in cortical parenchyma, The hairy covering consists of a few uniseriate 'trichomes. External glands do not occur on the leaf and axis.
Structure of the Axis.—The epidermis consists of small tabular cells with outer walls thickened and with lateral walls thin and undulated. The cortex is composed on the outer side of cork and on the inner side of chlorenchyma.
The sclerenchymatous pericycle is not developed. The wood is composite. Vessels are few, large and arranged in incomplete rows. The interfascicular wood prosenchyma is extensive and is formed of cells with thin walls and large lumina. Small groups of sclerenchyma enclose the lower ends of the xylem bundles. The medullary rays are uniseriate and numerous. There are numerous xylem bundles in the soft bast ring giving rise to slightly ribbed appearance to the axis. The pith is composed of thick-walled cells and is characterised by sieve-sclereids.
CELASTRACEAE.
Gymnosporia montana Benth.—'Figs. 86, 87. Upper epidermis locally two-layered. Lower epidermis formed of vertically elongated and papillose cells. Mesophyll consisting of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal glands consisting of cells with tanniniferous contents in the loaf and axis. Oxalate of lime not occurring in any form. Veins vertically transcurrent and enclosed in bundle-sheaths. Hairy covering absent. Pericycle composed of groups of stone-cells. Cork sub- epidermal. Wood prosenchyma formed of cells with thick walls and small lumina. Medullary rays 1-2 seriate. Pith heterogenous.
Structure of the Leaf.—The upper epidermis consists of tabular cells, with inner walls convexly arched inwards ; it is locally two- layered by division walls which may be thin or thickened and which are parallel to the surface of the leaf. The lower epidermis consists of polygonal cells which are greatly elongated vertically and are drawn out into papillae (fig. 86). Outer walls are thickened; inner walls are also thickened except in some cases, when the upper epidermal cells are divided by walls parallel to the surface. The lateral walls are thin and straight. The tendency to form a two-layered epidermis as well as the palisade-like elongation of the epidermal cells are adaptations to protect the palisade tissue against insolation as well as to check transpiration by depressing the stomata.
The stomata are numerous only on the lower surface and are surrounded by ordinary epidermal cells. The guard-cells are depress- ed and the front cavity is placed in a deep depression formed by the palisade-like surrounding cells.
The mesophyll is composed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. In the mesophyll there are numerous cells with tanniniferous contents. Secretory cells with tanniniferous contents are abundantly found in all tissues of the axis, Tanniniferous contents are found in cortical parenchyma, in cells separating the groups of stone-cells of the pericycle, in numerous cells in the soft bast and in the medullary ray cells which are opposed to the glandular cells between the pericyclic stone-cell groups. Oxalate of lime does not occur in any form in the leaf or axis.
The veins are enclosed in green bundle-sheaths and are vertically transcurrent above and below by colourless thick-walled parenchyma. There are small groups of stone-cells on the lower side of the phloem of larger veins, thus protecting it. Clothing as well as glandular hairs do not occur on the leaf and axis. The absence of a hairy covering is compensated for partly by the palisade-like elongated epidermal cells and partly by the two- layered epidermis.
Structure of the Axis.—The epidermis consists of small tabular cells with outer walls thickened. The cortex is composed on its outer side of an extensive cork tissue and on its inner side of glandular tissue already described (fig. 87).
The pericycle is composed of closely placed large groups of stone-cells separated by secretory cells with tanniniferous contents. The wood is composite (fig. 87). Vessels are fairly large and numerous. Interfascicular wood prosenchyma is composed of thin-walled cells with small lumina. The medullary rays are 1-2 seriate and are numerous, some of their cells holding tanniniferous contents.
The pith is heterogenous and is composed of groups of large elongated cells surrounding small cells (fig. 87).
RHAMNEAE.
Zizyphus jlljuba Lam. — Fig 88. Epidermis composed of hori- zontally tabular cells. Upper epidermis of the mid-rib grooved. Uniseriate trichomes more numerous on the lower surface. Secretory cavities not found in cortex. Pericycle formed of stone-cells. Long thin groups of stone-cells present in soft bast.
Zizyphus trinervia Roxb— Figs. 89, 90. Epidermis of the leaf composed of cubical or vertically tabular cells. Upper epidermis of the mid-rib not grooved. Uniseriate trichomes absent on the upper surface. Secretory cavities numerous in the cortex. Long thin groups of stone-cells found in soft bast. Pericycle formed of bast fibres.
Zizyphus rotundifolia Lam.—Figs. 91, 92. Epidermis of the leaf formed of cubical and vertically tabular cells. Upper epidermis of the mid-rib grooved. Uniseriate trichomes more numerous on the lower epidermis. Secretory cavities wanting in cortex. Stone-cells absent in soft bast. Pericycle formed of bast fibres.
Zizyphus truncata Blatt. and Hall. —Figs. 93, 94. Upper epidermis consisting of cubical and vertically tabular cells. Upper epidermis of the mid-rib not grooved. Uniseriate trichomes absent on the upper surface. Secretory cavities occurring in cortex. Stone-cells wanting in soft bast. Pericycle formed of bast fibres.
Structure of the Leaf:—The epidermis of the two surfaces differ in structure. The upper surface is smooth while the lower one is characterised by alternate ridges and furrows. The epidermal cells of the upper surface are larger and cubical or vertically tabular in all members (figs. 91, 93,) except Z. jiijuba where they are mostly horizontally tabular (fig. 88.) The outer walls are thickened and the lateral walls are thin and straight. The inner walls are thin and convexly arched inwards, so as to come into close contact with the assimilatory cells. Some of the upper epidermal cells are filled with yellowish brown contents of the nature of cellulose slime. The epidermal cells of bhe lower yurface are smaller and are horizontally tabular, the outer walls being thickened and the inner and lateral walls thin.
Stomata occur only on the lower surface and are mostly found on the ridges. Guard-cells are situated in the plane of surrounding cells and the front cavity is on a level with the surface.
The mesophyll is composed wholly of palisade cells which are more compact towards the upper surface and are somewhat loosely arranged towards the lower, especially so below the ridged where the stomata are mostly situated (fig. 93.) There are groups of palisade- like cells with faintly yellowish contents, usually above the veins. These perhaps function as water reservoirs. Cells with clustered crystals are numerous near the veins.
Internal glands are represented by groups of palisade-like cells on the upper side of the veins and by rounded cells near the veins, with faintly yellowish contents and functioning perhaps as water- storing tissue. Some of the upper epidermal cells hold faintly yellowish contents of the nature of the cellulose slime.
Secretory receptacles of lysigenous origin occur in the pith of all members and in the inner portion of primary cortex of Z. trinervia and Z. truncata. The secretory receptacles, as presented in T. S., are numerous and elongated in the former and rounded and few in the latter. The contents seem to be mucilaginous. The secretory receptacles in the pith are large and are lined by a layer of flattened cells resembling an epithelium. Some of the pith cells contain tannin.
Oxalate of lime occurs in the form of numerous clustered crystals in the neighbourhood of the veins.
The veins are embedded and have no distinct bundle-sheaths. There are numerous groups of water-storing tracheids at the termina- tions of the veins (fig. 93.) The veins of the mid-rib are vertically transcurrent above and below by collenchyma. The mid-rib is prominent below in all species ; it is grooved on the upper surface in Z.jujuba and Z. rotundifolia ; in the other species it is not grooved, the upper epidermis being composed of vertically elongated cells with inner and lateral walls thickened.
The epidermal cells of the lower side of the mid-rib and of the upper side, when it is not grooved, are small polygonal cells slightly thickened on all sides, thus adding to the rigidity of collenchyma above and below the veins of the mid-rib.
The hairy covering is composed of uniseriate trichomes (figs. 88, 93.) These are more numerous on the lower surface in Z. jujuba and Z. rotundifolia. In the other members they seem to occur on the upper surface only. Hairy covering on the axis consists of a few uniseriate trichomes as on the leaf. External glands are not found on leaf or axis.
Structure of the Axis : — The epidermis consists of small polygo- nal cells thickened on all sides. The primary cortex is characterised by the extensive development of subepidermal cork and by mucilagi- nous secretory cavities in Z. trinevia and Z. truncata.
The pericycle is composed of a composite and continous ring of bast fibres in all species except Z. jujuba, where it is represented by a composite and continuous ring of stone-cells. There are found long thin groups of stone-cells in the soft bast of Z. jujuba and Z. trinervia.
The wood forms a composite hollow cylinder in all species. The vessels are large having simple perforations and are arranged almost in complete rows. The interfascicular wood prosenchyma is exten- sive and is composed of cells with thick walls and small lumina The medullary rays are uniseriate and numerous.
The pith consists of thick-walled cells and is characterised by large mucilaginous secretory cavities. Some of the pith cells hold tanniniferous contents.
General Review : — The species of Zizyphus have the same struc- ture in the leaf and axis with certain differences which may be useful in the diagnosis of the species: —
1. Presence or absence of uniseriate trichomes on the upper surface of the leaf.
2. Shape of the upper epidermal cells.
3. Presence or absence of a groove on the upper epidermis of the mid-rib.
4. Pericycle formed of bast fibres or of stone-cells.
5. Presence or absence of stone-cells in soft bast.
SAPINDACEAE
Cardiospermum Halicacabum L— Fig. 95. Epidermal cells tabular with inner walls gelatinised. Stomata occurring on both the surfaces. Mesophyll formed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Cells with tanni- niferous contents in soft bast and pith. Oxalate of lime found in the leaf and axis. Leaf many-ribbed. Veins vertically transcurrent Clothing hairs unicellular or uniseriate. Glandular hairs formed of a short uniseriate stalk and of an ovoid curved head. Pericycle formed of a composite ring of stone-cells. Axis ribbed. Ribs strength- ened by collenchyma. Assimilatory tissue in the axis formed of chlorenchyma. Wood formed of xylem bundles connected by strands of interfascicular wood prosenchyma. Medullary rays absent. Pith formed of thin walled cells.
Structure of the Leaf : — The epidermis consists of tabular cells which are much larger on the upper surface. The outer walls are a little thickened ; the inner walls are gelatinised, and those of the upper epidermis are greatly arched convexly inwards. The lateral walls are very thin and straight. The gelatinisation of the inner walls of the epidermal cells compensates for the hairy covering which is scanty. The stomata are more numerous on the lower surface, and are surrounded by ordinary epidermal calls.
The mesophyll is composed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal secretory organs do not occur in the leaf. They are represented in the axis by secretory cells with tanniniferous contents in the soft bast and pith. Oxalate of lime occurs in the form of numerous clustered crystals near the veins in the leaf. The clustered crystals occur in a layer of cells outside the pericycle and in the pith of the axis.
The veins are provided with green bundle-sheaths. The leaves are many-ribbed and the veins of the ribs, which are prominent below, are vertically transcurrent above and below by collenchyma. The smaller veins are embedded.
The hairy covering consists of clothing and glandular hairs. The clothing hairs on the leaf are short, thick-walled, unicellular and with a sharp point. The clothing hairs on the axis are longer with muriculate walls; "the basal portion is divided by two to three cross- walls. The glandular hairs are formed of a short uniseriate stalk and of a small ovoid head which is curved and is divided by horizon- tal walls (fig. 95).
Structure of the Axis : — The axis is ribbed. The epidermal cells are small and vertically tabular with outer walls greatly thick- ened and convexly arched outwards. The primary cortex is formed of chlorenchyma which is bounded internally by a layer of thin- walled colourless cells mostly containing clustered crystals. Strands of collenchyma are developed in the ribs.
The pericycle is formed of a composite ring of stone-cells. The wood is composed of xylem bundles connected together by narrow strands of interfascicular wood prosenchyma formed of cells having thin walls and large lumina. The vessels are very large and have simple perforations. Medullary rays are absent. The pith consists of thin- walled cells.
MORINGASEAE
Moringa pterygosperma Gaert.-* Figs. 96, 97. Leaf. Water- storing cells vertically elongated, conspicuous and numerous in upper epidermis. Mesophyll formed of palisade tissue on the adaxial side and of spongy tissue on the abaxial side. Myrosin cells in the form of palisade-like cells and confined to the palisade tissue. Oxalate of lime absent. Veins enclosed in bundle-sheaths. Short unicellular clothing hairs occurring on both surfaces.
Moringa concanensis Nimmo: — Eig, 98. Leaf. Water-storing cells in upper epidermis few and formed of a little enlarged epider- mal cells. Lower epidermal cells with outer walls forming large papillae. Mesophyll composed of rows of palisade cells separated by myrosin cells on the adaxial side, and of armpalisade tissue on the abaxial side. Myrosin cells occurring between the rows of palisade cells as well as on the inner side of arm-palisade tissue. Clustered crystals of oxalate of lime numerous near veins and below lower epidermis. Veins not enclosed in bundle-sheaths but strengthened by arcs of stone-cells on their lower side. Hairs absent.
Structure of the Leaf : — The epidermis differs in structure on the two surfaces. The epidermal cells on the upper surface are tabular with outer and inner walls equally thickened and convexly arched outwards and inwards respectively. There are large water-storing cells, which are numerous and conspicuous in M. pterygosperma (fig. 96) intercalated amongst the ordinary epidermal cells, (figs. 96, 98). The epidermal cells on the lower surface are much smaller than those on the upper surface. The outer and inner walls are equally thickened and the latter are curved convexly outwards in the form of papillae which are very large in M. concanensis (fig. 96). Lateral walls are thin and straight.
Stomata occur only on the lower surface and are surrounded by ordinary epidermal cells. Guard-cells are situated quite below the plane of the epidermal cells. The front cavity is therefore placed in a pit as deep as the height of the epidermal cells ; air in these pits remains moist and transpiration is thus greatly diminished. This kind of contrivance is necessary in leaflets of species of Moringa which are not protected by a dense covering of hairs and which, on the other hand, are greatly shaken by wind, thus accelerating transpiration.
The hairy covering consists of a few short, thick-walled unicellu- lar clothing hairs found on both the surfaces of M. pterygosperma (fig. 96) ; it does not occur in M. concanensis. External glands are absent. The mesophyll differs in structure in the two species. In M. pterygosperma (fig. 9G) it is composed of palisade tissue on the adaxial side and of spongy tissue on the abaxial side. In M. concanensis (fig. 98) the palisade tissue occurs on the upper side and is composed of rows of palisade cells separated by greatly elongated myrosin cells ; a single layer of arm-palisade cells occurs below the lower epidermis.
Internal secretory organs are abundantly developed, in the mesophyll of M. concanensis (fig. 98G.) They are partly composed of greatly elongated tabular cells between the rows of palisade cells and partly of horizontally elongated polygonal cells forming a more or less continuous layer on the inner side of the arm-palisade tissue. Secretory cells in M. pterygosperma (fig. 96G) are abundant in the palisade tissue and are repersented by palisade-like cells. Internal secretory cells hold yellowish brown contents and seem to be of the nature of myrosin cells.
Oxalate of lime occurs in the form of numerous clustered crystals near the veins and below the lower epidermis of M. concanensis. It is not found in M. pterygosperma.
Veins are embedded in both the 'species. They are enclosed in green bundle-sheaths in M. pterygosperma ; they are strengthened by arcs of stone-cells on their lower side in M. concanensis.
PAPILLIONACEAE
Heylandia latebrosa DC— Fig. 99. Epidermal cells poly- gonal. Large water-storing cells intercalated amongst ordinary epi- dermal cells. Mesophyll bifacial. Veins vertically transcurrent by sclerenchyma. Tannin sacs absent. Clothing hairs in the form of uniseriate trichomes with muriculate walls. External glands absent. Assimilatory tissue in the axis chlorenchymatous. Pericycle formed of bast fibres. Medullary rays uniseriate. Pith formed of thin- walled cells.
Crotalaria Burhia Ham.— Figs. 100, 101. Epidermal cells polygonal with lateral walls undulated. Large water-storing cells intercalated amongst ordinary epidermal cells. Mesophyll isobila- teral. Veins embedded and enclosed in bundlesheaths. Tannin sacs found near the veins. Clothing hairs in the form of uniseriate tricho- mes with muriculate walls. External glands absent. Assimilatory tissue in the axis formed of palisade cells. Pericycle formed of stone-cells. Medullary rays uniseriate. Pith formed of thin-walled cells. Cortical vascular bundles present.
(To be continued.)
Plate IX
68-70. Tribulus terrestris.
68. T. S. of the leaf. Oc. 1 ; Ob. 3 mm. Ap.
69. Hair on the leaf.
Oc. 1 ; Ob. 3 mm. Ap.
70. T. S. of the axis- Oc. 3 ; Ob. C.
71-74. Seetzenia orientalis.
71. T. S. of the leaf. Oc. 1 ; Ob. 3 mm. Ap.
72. Stoma on the leaf. Oc. 4 ; Ob. 3 mm. Ap.
73. T. S. of the axis. Oc. 4 ; Ob. C.
74. 75. Zygophyllum simplex. T. S. of the leaf. Oc. 3 ; Ob. A.
N.B.— To get the original dimensions multiply by 1*7, 
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Plate X
76. Zygophyllum simplex. 80. Glandular hair on the leaf
T. S. of the axis. Oc. 6;Com. ; Ob. 3 mm. Ap.
Oc. 1 ; Ob. 3 mm. Ap. 81. Hair on the leaf.
77-78. Fagbnia cretica. Oc. 2 Com. : Ob. 3 mm. Ap.
77. I. S of the leaf. 82-84. Balanites Boeburghii. Oc. 2 ; Ob. C. 82. T. S. of the leaf.
78. T. S. of the axis. Oc. 6 Com. ; Ob. 8 mm. Ap. Oc. 3 ; Ob. C. 83. T. S. of the axis.
79-81. Monsonia heliotropioides. Oc. 6 Com. ; Ob. 8mm. Ap.
79. T. S. of the leaf. 84. Stoma on the leaf.
Oc. 6 Com. : Ob. 8 mm. Ap. Oc. 6 Com. ; Ob. 3 mm. Ap.
N.B. — To get the original dimensions multiply by V7. 
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Plate XI
85. Commiphora Muhul.
T. S. of the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap. 86-87. GymnoSporia montana-
86. T. S. of the leaf.
Oc. 6 Com. : Ob. 8 mm. Ap.
87. T. S. of the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap. 88. Zizyphus jujuba.
T. S. of the leaf.
Oc. 3 ; Ob. C. 89-90. Zizyphus trincrvia. 89. Hair on the leaf.
Oc. 3 ; Ob. 7
90 T. S. of the leaf. Oc 3;Ob.C. 91-92. Zizyphus rotundifolia.
91. T. S. of the leaf. Oc. 3 ; Ob. C.
92. T. S of the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap. 93-94. Zizyphus truncata.
93. T. S. of the leaf. Oc. 1 ; Ob. C.
94. T. S. of the axis Oc. 4 Com. ; Ob. 3 mm. Ap.
N.B* — To get the original dimensions multiply by 1'7. ,_Plants_of_the_Indian_Desert.jpg)
Plate XII
95. Cardiospermum Halicacabum. T. S. of the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap. 96-97 Moringa pterygoeperma.
96. T. S. of the ieaf.
Oo. 6 Com. : Ob. 8 mm, Ap.
97. Stoma on the leaf.
Oc. 6 Com. ; Ob, 3 mm. Ap
98. Moringa concanensis. T. S. of the leaf.
Oc. 6 Com. ; Ob. 8 mm. Ap.
99. Heylandia latebrosa.
T. 8. of the leaf showing epider- mis. Oc. 6 Com. : Ob. 8 mm. Ap.
100-101. Croialaria Burkia.
100 T. S. of the leaf.
Oc. 6 Com. : Ob. 8 mm. Ap.
101 T. S. of the axis.
Oc. 2 com, ; Ob. 8 mm. Ap. 102-103 Croialaria medicaginea.
102. T. S. of the axis.
Oc. 6 Com. ; Ob. 8 mm. Ap.
103. Hair on the axis.
Oc. 6 Com. ; Ob. 3 mm. Ap. 104. Indigo/era cordifolia. T. S. of the leaf.
Oc. 4 Com. ; Ob. 3 mm. Ap.
N.B. — To get the original dimensions multiply by 1*7. 
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